[Virtio-fs] [PATCH 2/4] virtiofsd: add --print-capabilities option

[Stefan Hajnoczi]

Add the --print-capabilities option as per vhost-user.rst "Backend
programs conventions".  Currently there are no advertised features.

Signed-off-by: Stefan Hajnoczi <stefanha at redhat.com>
---
 docs/interop/vhost-user.json       |  4 +++-
 contrib/virtiofsd/fuse_lowlevel.h  |  1 +
 contrib/virtiofsd/helper.c         |  2 ++
 contrib/virtiofsd/passthrough_ll.c | 12 ++++++++++++
 4 files changed, 18 insertions(+), 1 deletion(-)

diff --git a/docs/interop/vhost-user.json b/docs/interop/vhost-user.json
index da6aaf51c8..d4ea1f7ac5 100644
--- a/docs/interop/vhost-user.json
+++ b/docs/interop/vhost-user.json
@@ -31,6 +31,7 @@
 # @rproc-serial: virtio remoteproc serial link
 # @scsi: virtio scsi
 # @vsock: virtio vsock transport
+# @fs: virtio fs (since 4.2)
 #
 # Since: 4.0
 ##
@@ -50,7 +51,8 @@
       'rpmsg',
       'rproc-serial',
       'scsi',
-      'vsock'
+      'vsock',
+      'fs'
   ]
 }
 
diff --git a/contrib/virtiofsd/fuse_lowlevel.h b/contrib/virtiofsd/fuse_lowlevel.h
index b441d3dfed..e3d8747571 100644
--- a/contrib/virtiofsd/fuse_lowlevel.h
+++ b/contrib/virtiofsd/fuse_lowlevel.h
@@ -1796,6 +1796,7 @@ struct fuse_cmdline_opts {
 	int nodefault_subtype;
 	int show_version;
 	int show_help;
+	int print_capabilities;
 	int clone_fd;
 	int syslog;
 	int log_level;
diff --git a/contrib/virtiofsd/helper.c b/contrib/virtiofsd/helper.c
index 8d8bca889b..84bf1c834d 100644
--- a/contrib/virtiofsd/helper.c
+++ b/contrib/virtiofsd/helper.c
@@ -35,6 +35,7 @@ static const struct fuse_opt fuse_helper_opts[] = {
 	FUSE_HELPER_OPT("--help",	show_help),
 	FUSE_HELPER_OPT("-V",		show_version),
 	FUSE_HELPER_OPT("--version",	show_version),
+	FUSE_HELPER_OPT("--print-capabilities", print_capabilities),
 	FUSE_HELPER_OPT("-d",		debug),
 	FUSE_HELPER_OPT("debug",	debug),
 	FUSE_HELPER_OPT("-d",		foreground),
@@ -137,6 +138,7 @@ void fuse_cmdline_help(void)
 {
 	printf("    -h   --help                print help\n"
 	       "    -V   --version             print version\n"
+	       "    --print-capabilities       print vhost-user.json\n"
 	       "    -d   -o debug              enable debug output (implies -f)\n"
 	       "    --syslog                   log to syslog (default stderr)\n"
 	       "    -f                         foreground operation\n"
diff --git a/contrib/virtiofsd/passthrough_ll.c b/contrib/virtiofsd/passthrough_ll.c
index 0ef01b7e3f..e2e20f22cd 100644
--- a/contrib/virtiofsd/passthrough_ll.c
+++ b/contrib/virtiofsd/passthrough_ll.c
@@ -2879,6 +2879,14 @@ static void fuse_lo_data_cleanup(struct lo_data *lo)
         free((char *)lo->source);
 }
 
+/* Print vhost-user.json backend program capabilities */
+static void print_capabilities(void)
+{
+	printf("{\n");
+	printf("  \"type\": \"fs\"\n");
+	printf("}\n");
+}
+
 int main(int argc, char *argv[])
 {
 	struct fuse_args args = FUSE_ARGS_INIT(argc, argv);
@@ -2931,6 +2939,10 @@ int main(int argc, char *argv[])
 		fuse_lowlevel_version();
 		ret = 0;
 		goto err_out1;
+	} else if (opts.print_capabilities) {
+		print_capabilities();
+		ret = 0;
+		goto err_out1;
 	}
 
 	if (fuse_opt_parse(&args, &lo, lo_opts, NULL)== -1)
-- 
2.21.0